The mechanism behind the formation of a dye image in a silver halide color photographic material is as follows: an aromatic primary amino color developing agent reduces silver halide grains in the exposed photographic material; at the same time, the developing agent is oxidized and the resulting oxidation product reacts with a built-in coupler to form a dye. Since color reproduction depends on the substractive process, three couplers are customarily used to form yellow, magenta and cyan dyes.
Magenta dye images are formed by 5-pyrazolone, cyano-acetopnenone, indazolone, pyrazolobenzimidazole and pyrazolotriazole couplers. Most of the magenta dye image forming couplers used commercially today are 5-pyrazolone compounds. The dye image formed from the 5-pyrazolone couplers have high resistance to both light and heat but, on the other hand, the image does not exhibit a satisfactory color tone and presents an unwanted absorption in the yellow component around 430 nm. Furthermore, the relatively long tail at the long wavelength side causes color contamination. Because of these defects in spectral absorption characteristics, the color dye image resulting from the 5-pyrazolone couplers lacks brightness.
This has presented a particularly serious problem for direct viewing color prints wherein the image is supported on a reflective base. Couplers from which unwanted absorptions are eliminated have been proposed and those described in U.S. Pat. No. 3,725,067, Unexamined Published Japanese Patent Application Nos. 99437/1984, 162548/1984, 171956/1984, Research Disclosure Nos. 24220, 24230 and 24531 have excellent performance. However, the dye images formed from these couplers have a very low degree of light fastness, and if they are incorporated in photographic materials for direct viewing prints, the essential needs of photographic materials for recording and preserving images cannot be satisfied.
With a view to improving the light fastness of color images formed from 1H-pyrazolo[5,1-c]-1,2,4-triazole type couplers, Unexamined Published Japanese Patent Application No. 125732/1984 and Research Disclosure No. 24531 proposed the use of a pholic or phenol ester antioxidant. However, these compounds will often cause color changes and fogging and do not have satisfactory physical properties with respect to dispersibility and crystallization. In addition, these compounds are not completely effective against discoloration and hence fail to provide color images having the desired light fastness.
Oxygen is known to be one of the causes for deterioration of the light fastness of color dye images, and it has been proposed that improved light fastness can be achieved by isolating the color dye image from oxygen. For example, Unexamined Published Japanese Patent Application Nos. 11330/1974 and 57223/1975 describe methods for enclosing the color dye image with an oxygen blocking layer made of a material with low oxygen permeability (e.g., by laminating the image with a polyester layer). These methods are effective to some extent but are far from being satisfactory in that the light fastness of the image formed from certain couplers is deteriorated rather than improved. An additional disadvantage is the increase in the number of steps involved, which makes the overall process complicated and costly.